Flexible cellulosic articles having ultra-violet light shielding properties and method of producing them



SEARCH ROOM vMarch 14, 1967 w. T. BRADER, JR.. ETAL 3 309 2l FLEXIIBLE CELLULOSIC ARTICLES HAVING ULTRA-VIOLET LIGHT g SH ELDING PROPERTIES AND METHOD OF PRODUCING THEM R MISSING XR Filed Deo. z8, 1962 United Statesl Patent 3,309,2i8' Patented Mar. 14, 1967 dice FLEXIBLE CELLULOSIC ARTICLES HAVING ERTIES AND METl-IOD 0l? PRODUCING Wilbur T. Bradcr, Jr., Swarthmore, Pa., and Thomas E.

Bradley, Wilmington, Del., assignors, by mesne assignments, to FMC Corporation, San Jose, Calif., a corporation of Delaware Filed Dee. 28, 1962, Ser. No.'247,954 1t) Claims. (Cl. 11T-33.3)

This application is a continuation-in-part of application Ser. No. 180,328, filed Mar. 3, 1962, and now abandoned.

This invention relates todliblehhghjop articles which afford improved, ultra-yiolet` sht pro cction and a method for producing the same, More particularly, it' relates to hydrophilic eellulosic films which may or may not have an appreciable orange color and which demonstrate substantially reduced` transmission of light rays in the ultra-violet range.n

Food products which contain fats and oils are quickly degraded when subjected to light containing ultraviolet rays. Packaging materials which provide improved shielding of ultra-violet light sensitive materials, particularly fatty or oily foods, are in demand. ln many instances it is preferred or required that the packaging materials be clear and colorless while affording the desired U.V. protection.

A serious problem relating to cellulosic films and sheets containing U.V. shielding7 material or coloring material, particularly those used for wrapping fods, is the lack of stability of suitable U.V. shielding and/or coloring agents. Transparent non-fibrous cellulosic sheets, Stich as regenerated cellulose films, are extensively used for food wrapping including bakery products and meat products.

Fibrous cellulosic casings are used extensively to encase ground meat products. It is essential that any shielding and/'or coloring agent employed for these wrapping materials remain in or on the sheets and not migrate into the food contained therein. While a problem exists in obtaining a shielding and/or coloring agent which has the necessary stability under moist conditions, it is also extremely difficult to obtain such a material which meets the safety standards of state 'and Federal food and drug agencies.

Colored pack iging material is often used to provide a d`stinctivc package for the wrapping of foods and other items. ln addition, the color may act to protect the packaged item from damaging low wave length light 'tlVCS.

lt is an object of this invention to provide tlexible ccllulosic material` containing an ultra-violet light shielding substance which is stable iutlie presence of moisture and`has either yno appreciable'color or a commercially desirable orangt color.

lt is another object of the invention to provide a method of obtaining ultra-violet light shielding, nontibrousfcellulosic sheets.

lt is another object of this invention to provide a method for obtaining a clear orange-colored regenerated cellulose film which is stable in the presence of aqueous and olcaginous mediums and has excellent ultra-violet light shielding properties.

lt is another object of this invention to provide a package including a wrapping sheet having improved ultra-violet light shielding properties.

These and other objects are accomplished in accordance with this invention by providing a hydrophilic flex- .ible ccllulosic article uniformly impregnated with hydrated bromide, ferrie nitrate, and ferrie sulfate.

ferrie oxide or ferrie hydroxide` and a method of producing a hydrophilic flexible cellulosic article having improved ultra-violet light shielding properties which comprises treating said article with an aqueous solution of an inorganic water-soluble lerric salt and then immersing said article in an aqueous solution maintained at a pH. of at least 5.

ln addition, this invention includes a package comprising ultra-violet light sensitive material and a wrapping sheet at least partially encompassing said material comprising a hydrophilic flexible cellulosic sheet uniformly impregnated with ferrie hydroxide.

Flexible cellulosic articles of this invention include, for example, fibrous and non-fibrous sheets, foils, hlms, pelliclesribbons, monof'ilament, multifllamcnt yarn, staple fiber, cord, and similar articles. Examples of` the hydrophilic cellulosic materials are regenerated cellulose, cellulose ethers including carboxy-methyl cellulose, hydrophilic cellulose esters, cotton, paper, etc. The preferred form of this invention concerns clear, non-fibrous hydrophilic cellulosic sheets and brous base sheets impregnated with hydrophilic ccllulosic film-forming material.

Water-soluble inorganic ferrie salts are well known substances and include for example, ferrie chloride, ferrie Of these materials ferrie chloride is preferred since it gives thc best results under varying process conditions.

The flexible cellulosic article is introduced into a bath of the aqueous solution of inorganic water-soluble ferrie salt which is maintaiucd'at a salt concentration ranging from about 0.01 to about 15% depending upon the desired U.V. protection and/or shade of color which is to be produced on the finished article. ln the case of clear, food packaging material a concentration of about 5% will produce a conventional amber-colored hlm while a concentration of less than about 0.2% will produce a film having UN. light shielding properties without appreciable color.

It is preferred for the method of this invention that the cellulosic article is first wet prior to treatment with the ferrie salt solution. In the case of regenerated cellulose hlm, for example, it is convenient to run the wet gel film into a ferric Salt bath as it comes from the film spinning machine.

The temperature of the ferrie salt bath is not critical and generally is maintained at about room temperature. The immersion time for the eellulesic material in the ferrie salt bath can range from as low as about l second to as high as about 60 seconds in order to produce successful results.

After being impregnated with the aqueous ferrie salt solution, the excess solution is removed with rollers, scrapcrs, doctor blades and the like from the cellulosic article and it is then inuncrsed in an aqueous solution which is maintained at a pi-l ol' at least 5 and preferably at least l0. At a pl-l of 5 it can be seen that the hydrated ferrie oxide, or ferrie hydroxide begins to precipitate within the ccllulosic material` lt is necessary, however, for a commercially suitable process that the pl'l of the second bath be maintained at at least l0 or higher. This is accomplished by continually introducing a basic matcrial or solution into the second bath. This basic material preferably includes an alkali or alkaline earth metal basic salt or hydroxide, and most preferably sodium hydroxide. Other basic materials include for example, sodium acctate, sodium carbonate. ammonium hydroxide, potassium hydroxide, calcium hydroxide, ctc. Care must be taken to keep the concentration of the basic material low enough to prevent hydrolysis of the cellulosic material. The temperature of'this second bath is not critical and is generally maintained between room temperature and about 40 C The article is permitted to remain in the second bath for at least seconds up to about 30 seconds to precipitate ferrie oxide within it. After removal from the second bath the excess basic material can be washed olf with rcopious amounts of fresh water.

ln the case of cellulosic sheets and films, particularly non-fibrous films, plasticization may be accomplished after removal of excess base therefrom. The usual plasticizcrs including glycerol are useful and are incorporated in an aqueous hath through which the cellulosic sheet is i'un. Anchoring agents, which promote adhesion -between the base film and polymeric film-forming coatings which may be applied, are conveniently incorporated in the plasticizing bath. Anchoring agents include, for example, melamine-formaldehyde precondensates, ureatormaldehyde prccondensates, polyalkylenimines, epoxy resins, etc. 1f these materials are not water-soluble they may be applied to the base sheet after drying.

The polymeric film-forming coatings which may be used for this invention include, for example, copolymers of at least 50% vinylidene chloride and at least one other monomer copolynierizable therewith, vinylchloride-vinyl acetate copolymers, nitrocellulose, polyalkylcnes such as polyethylene and polypropylene, etc. These coatings may :he applied by melt extrusion or from solutions, including lacquers and latexes, to the colored cellulosic base sheet.

The following examples are set forth to demonstrate the -articles of this invention and methods of making them.

Example I A wet gel regenerated cellulose film is first treated in a hath containing an aqueous solution of 5% by weight of ferrie chloride at a bath temperature of 25 C. The film is immersed in the bath for l5 seconds, then removed, and the excess bath solution removed by ruiming the film through a pair of squeeze rollers. The wet film is then treated in a bath containing an aqueous solution of 2% by weight of sodium hydroxide at a bath temperature of 50 C. After 15 seconds immersion the film is removed from the bath. The film is washed many times with copious amounts of fresh water to remove any sodium hydroxide solution. The film has a clear, uniform amber color.

In order to produce a film which may be coated with a inoisturcproof coating it is next plasticized and anchor treated by running the film through a bath containing an aqueous solution of 5% by weight of glycerol and 0.26% by weight of a melamineformaldehyde precondcnsate resin. The immersion time in this hath is about seconds. The film is then heat dried for 3 minutes at 90 C.

This film has a clear, uniform amber color. Films produced substantially as described above show no visible bleeding in water at 50 C. when immersed for one minute.

Films produced in this manner were exposed to various test conditions to determine their stability. Extraction tests were conducted by placing lialf-inch squares cut from one gram of the tilm in glass-stoppercd, Erlenmeyer flasks containing various extracting media at C. Results of these extraction tests after two and one-half days were as follows.

TABLE l lxtraction medium: ("olor of extract Distilled water Colorless. 3% sodium bicarbonate Very,` very slight. 3% ethanol Colorlcss. Corn oil No color change.

In addition, Colored film samples were exposed to bacon and Cashew nuts overnight. One piece of the colored film was wrapped about a few slices of fatty bacon.

This was then ovcrwrapped with moistureproofed cello- 4 packets containing lead shot placed on top. In the case of both the bacon and the cashew nuts no bleeding of the coloring was observed.

Colored regenerated cellulose hlm which had been plasticized and anchor coated as described above was coated with a Saran coating. The coating was prepared from a coating lacquer comprising about 20% of a copolymer of by weight of vinylideiie chloride and 10% of aerylonitrile dissolved in a mixture of about 60 parts tetrahydrofuran and 40 parts of toluene. In addition to the copolymer, the coating also contained small proportions of clay, wax and an alkyd resin to promote better surface characteristics. The above coating composition and lacquer coating technique are conventionally used to coat cellophane hlm. Anchorage tests were run on the Saran coated, colored regenerated cellulose film and Saran coated, uncolored film for comparison with the following results.

In the above physical tests, the Tape Pull test is a incasure of adhesion strength and involves impressing a 4 inch by 1 inch cellophane adhesive tape on the coating and then tearing the tape from the coated surface. The amount of coating removed is noted and the adhesion property rated.

The Heat Seal test is well known in the coated film art and, in general, involves heat sealing two strips of the same test film together and then measuring the strength necessary to pull them apart on a standard test machine.

The Wet Anchorage test is a procedure used to determine how well the coating will remain adhered to the -base film after exposure to excess moisture. ln the test, the sample film is immersed in water at room temperature for 17 hours. The sample is then removed and rubbed vigorously between the fingers in an attempt to remove the coating.

. Finally, the Boiling Water tes-t is used to determine anchorage strength under severe conditions. ln thisl test', strips of the saaie test sample are heat sealed together to provide a two inch seal. One ofthe strips has had a section of coating removed therefrom and the other strip positioned so that it will pull against an exposed edge of the coating when the two strips are pulled apart. The ends of each strip are left unsealed and one of these ends is clamped to a fixed position. The other' end has a free hanging weight clamped thereto and the heat sealed portion is immersed in boiling water. At the time of imniersion a stop watch is started and the length of time necessary to'strip the two inches of coating is recorded.

lt was noted that the coatings on the colored lilniof ythis invention have unexpectedly higher adhesion ratings than similar coatings have to the uncolored film.

Example Il Wet gel regenerated film samples were dipped respectively in aqueous baths of low concentrations of FeCl3 ranging from 0.05 to l.0% of the anhydrous saltl The gel films were dipped in these baths at 25 C. for l5 seconds. Excess solution was removed by blotting between paper towels and running the films through a wriiiger. They were then immersed in a 2% aqueous sodium hydroxide bath at 50 C. for 15 seconds. The lilms were then thoroughly water washed,'plasticized and anchor coated with a second treatment in a 5% glycerol bath containing 0.26% melamine-formatdehyde precondensate. They were then air dried in wooden frames.

Analysis of light transmissions of these sample films were made and the data obtained are shown in graph form in FIG. 1 of the accompanying drawing. lty can -be seen from the curves of the graph that considerable protection is obtained in the ultraviolet light ray range o'f from 2400-4000 A. with films containing low amounts of ferrie hydroxide. Film 2 treated with 0.05% FcCl3 has a reduced ultra-violet light transmission of over 40% while film 3 treated with a 0.2% FeClg solution has a reduced transmission of over 56% at 3200 A. compared to film 1 which is untreated regenerated cellulose film. The film which has been treated with the 0.05% solution of FeCl3 has no appreciable yellow or orange color. Films treated with 0.2% FeCl3 solution have a very light yellow tint and the shade of the color increases in those which have been treated with solutions ot increased strength. The ultra-violet light protection also increases with higher bath concentrations.

This appreciable ultra-violet light (U.V.).protection with films containing sufliciently low concentrations of Fc(Oli)3 to provide little or no color is entirely unexpected in view of unsuccessful attempts to obtain U.V. protection by precipitating other metal hydroxidcs in films with and without coloring. Al(OH)3, Mg(OH)2 and Zr(O1-I).,l were incorporated into regenerated eellulose films to produce clear films with practically no absorbenee of U.V. wave lengths.

In FIG. 2 of the drawing a comparison of the U.V. protection Obtained from certain wrapping materials is shown. The direct dyed Tango film is a commercially available regenerated cellulose film dyed to an orangetan color with an organic dye. Glassine paper is a commercially available material prepared by the addition of a urea-formaldehyde resin to a thin transparent. paper. The new Tango hlm is an article of this invention comprising regenerated cellulose film impregnated with Fe(OH)3 hy rst treating with a 5% aqueous solution of FeCl3 and then with 2% aqueous solution of sodium hydroxide. The high degree of U.V. protection obtained with the film of this invention is entirely unexpected.

Packages of fatty and oily food products prepared with the Fe(OH)3 impregnated tilms of this invention provide appreciable improvement in the protection ofthe wrapped food from the harmful cfTects of alta-violet light radiation when exposed to direct sunlight over packages prepared with untreated films of the sante base material.

Fe(OH)3 impregnated sheets may be used to overwrap packages or may he placed in direct. contact with the food product. These films may also be used as the transparent window material in packages or boxes manufactured with opaque packaging materials.

Various changes and modifications may be made in practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

We claim:

1. A.\vrappng material for an ultra-violet light sensitive article comprising a clear, non-fibrous regenerated Cil cclltrlose shect uniformly impregnated with ferrie hydroxide in an amount sullicient to improve thc ultraviolet light shielding properties of said sheet.

2. The sheet of claim 1 having a film-forming polymer coating on the surface thereof.

3. The sheet of claim 2 -wherein the film-forming polymer is a copolymer of at least of vinylidcne chloride and at least one other monomer copolymerizable therewith.

4. A method oi preparing a flexible hydrophilic, nonfibrous cellulosic sheet having improved ultra-violet light shielding properties which comprises treating said article with an aqueous solution of an inorganic water-soluble ferrie salt and then immcrsing said article in an inorganic water-soluble ferrie salt and then immcrsing said article in an aqueous solution maintained at a pH of: at least 5 to precipia-te ferrie hydroxide in situ.

5. The method of claim 4 wherein the plt is maintained at least 10.

6. A method of preparing a flexible hydrophilic, nontibrous cellulosic sheet having improved ultra-violet light shielding properties which comprises treating said sheet with an aqueous solution of an inorganic water-soluble ferrie salt, and then immcrsing said sheet in a bath containing an aqueous solution of a water-soluble compound selected from the group consisting of alkali and alkaline earth metal basic salts and hydroxides, said solution maintained ata pH of at least l0.

7. The method of claim 6 wherein the water-soluble ferrie salt is ferrie chloride and the water-soluble compound is sodium hydroxide.

tt. A continuous method of preparing a flexible, hydrophilic, non-fibrous cellulosic sheet having improved ultraviolet light shiclding properties which comprises treating said sheet with an aqueous solution containing from about i 0.01 to about 10% by weight of ferrie chloride, removing excess ferrie chloride solution from the sheet, and then immcrsing said sheet in an aqueous solution containing about 2% by weight of sodium hydroxide and maintaining the sodium hydroxide solution at a pl-t of at least 10.

9. The method of claim 8 wherein the flexible cellulose sheet is a clear regenerated cellulose film.

10. The method of claim 8 wherein the flexible cellulosic sheet is a clear carboxymethyl cellulose ether hlm.

References Cited by the Examiner UNlTED STATES PATENTS 2,380,775 7/1965 Meyer 117-169 X 2,461,522 2/1949 ce@ 99-174 X roattoN PATENTS 730,601 5/1955 Great Britain.

OTHER REFERENCES Gregory, Uses and Applications of Chemical and Related Materials, Reinhold, N.Y., 1939, pages 284-287. WILLIAM D. MARTlN, Prlrzal'y Examiner.

H. W. MYLIUS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,309,218 March 14, 1967 Wilbur T. Bradr, Jr., et a1.

It is hereby certified that error appears in the above numbered pat.- ent requiring correction and that the seid Lettera Patent should reed as corrected below.

Column 1, line 32, for "fods" read foods column b, lines 14, 1S and 16, strike out "inorganic water-soluble ferrc salt and then mmersng sald article in an"; line 19, for "at least 10." read at at least 10. line 48, for 7/1965" read 7/1945 Signed and sealed this 10'th day of'October 1967.

(SEAL) Auen.'

EDWARD J. BRENNER Commaconcr of Pllenu Edwnrd M. Fletcher, Jr.

Attesng Officer 

1. A WRAPPING MATERIAL FOR AN ULTRA-VIOLET LIGHT SENSITIVE ARTICLE COMPRISING A CLEAR, NON-FIBROUS REGENERATED CELLULOSE SHEET UNIFORMLY IMPREGNATED WITH FERRIC HYDROXIDE IN AN AMOUNT SUFFICIENT TO IMPROVE THE ULTRAVIOLET LIGHT SHIELDING PROPERTIES OF SAID SHEET. 